Summary The pilot of a Cessna 172D, C-FBVW, with one passenger on board, was conducting left-hand circuits to runway 32 at 108 Mile Airport. Shortly after C-FBVW turned onto final and descended toward the runway, the aircraft collided with a second Cessna 172, C-GWAC, which was inbound to the airport from the south on an established straight-in approach to the same runway. The collision took place at about 300 feet above ground level. Both aircraft were locked together by the collision and became uncontrollable. They descended at a steep angle and crashed into the corner of a warehouse building at the south end of the 108 Mile shopping centre. The shopping centre is about 2 000 feet south of the approach end of the runway and about 500 feet east of the runway's extended centre-line. The three people involved in this in-flight collision were seriously injured by impact forces but were rescued by first responders. There was no fire. Ce rapport est galement disponible en franais. Other Factual Information The pilots of both aircraft were certified and qualified, and there was no evidence that any physiological factors affected their ability to conduct the flights safely. There were no mechanical discrepancies found with either aircraft that would have contributed to the occurrence. The 108 Mile Airport is a registered, uncontrolled aerodrome, at an elevation of 3 127 feet above sea level (asl), operated by the Caribou Regional District. The aerodrome has a single, asphalt runway 4 877 feet long by 75 feet wide, oriented on a 320/140 degree magnetic heading. The aerodrome traffic frequency (ATF) is 123.2 megahertz and is used within a radius of 5 nautical miles and to an altitude of 6 100 feet asl. A.I.P. Canada, published by Transport Canada (TC), prescribes the procedures that pilots should follow when operating at an uncontrolled airport. These procedures are widely distributed and establish a fundamental basis for safe aircraft operations in Canada. Prior to joining a traffic circuit, all pilots should announce their intentions. Where no mandatory frequency (MF) procedures are in effect, aircraft should approach the traffic circuit from the upwind side or, once having ascertained without any doubt that there will be no conflict with other traffic entering the circuit or established within the circuit, the aircraft may join the circuit on the downwind leg. There are no MF procedures in effect at 108 Mile Airport. Designation of an ATF is aimed at ensuring that all radio-equipped aircraft operating on the ground or within the specified ATF area are listening on a common frequency and following common reporting procedures. Figure 1 -Standard Right-Hand Circuit at 108 Mile Airport Canadian Aviation Regulations require that all turns be to the left while operating in the circuit, unless a right-hand circuit has been specified in the Canada Flight Supplement (CFS). The CFS specifies right-hand circuits for runway 32 at 108 Mile Airport during daylight hours. The pilot of C-FBVW had flown to 108 Mile Airport from Prince George on the day before the accident and had remained in the area overnight. He planned to continue his trip to Vernon on the morning of the accident and had called the Kamloops Flight Service Station for a weather briefing. Based on the content of that briefing, he concluded that the en route weather in the vicinity of Bonaparte Lake was below the minimum required for visual flight rules (VFR) flight and he decided to delay his departure until the weather improved later in the day. At 1100 Pacific daylight time (PDT),(1) he decided to do some local flying while waiting for an improvement in the weather to the south. The wind at 108 Mile Airport was light out of the northwest, and the pilot and his one passenger (who also held a valid private pilot's licence) took off from runway 14 with a slight tail wind. The pilot was flying the aircraft from the right-hand seat. His passenger was wearing the only available headset and was handling the radio work associated with the flight. This assignment of work was required because the headset connected to the aircraft dash on the left side of the aircraft. The aircraft was equipped with navigation lights and a landing light, neither of which were on at the time of the accident. The pilot did several left-hand circuits on runway 14 and then proceeded to 100 Mile House, about eight miles to the south. He overflew that aerodrome, assessed that the runway and wind conditions were unsuitable for a landing, and completed a left turn back toward 108 Mile Airport. That turn placed the aircraft to the east of Highway 97, as well as to the east of the extended centre-line of runway 32 at 108 Mile Airport. He approached 108 Mile Airport from the southeast and crossed the aerodrome at midfield about 1 000 feet above the aerodrome elevation. After he crossed the airfield, he turned left to join downwind, left-hand for runway 32. His passenger made radio calls before entering the ATF area, when crossing midfield, and when established on final for runway 32 and did not hear any radio calls from any other aircraft in the vicinity. The pilot of C-FBVW completed a touch-and-go landing from this first circuit, then entered into a second left-hand circuit for runway 32. His passenger reportedly made radio calls downwind and on turning final; again she heard no response from any other aircraft. It was following the completion of the final turn on this second circuit that C-FBVW was involved in a mid-air collision. C-FBVW descended onto C-GWAC, which was completing a straight-in approach to runway 32. The pilot of C-GWAC had filed a VFR flight plan from Merritt to his destination of 100 Mile House. When he reached 100 Mile House, the pilot decided to overfly that aerodrome and to continue on to 108 Mile Airport. He reportedly made a radio call prior to entering the 108 Mile Airport ATF area, using a handheld radio that he carried in the breast pocket of his shirt. He reported that he was setting up for a straight-in approach to runway 32. He did not hear any response from any other aircraft in the area and continued inbound to the airport. During the straight-in approach, the pilot concentrated his lookout upwards and to the right, in anticipation of any unannounced traffic that may have been operating in a right-hand traffic pattern. While on short final to runway 32, C-GWAC was involved in a mid-air collision when it was struck from above by C-FBVW. C-GWAC was equipped with navigation lights, a rotating anticollision light, and a landing light. The first two of these lighting systems were operating at the time of the collision, but the landing light was selected off. A post-crash examination of the handheld radio showed that the correct ATF was not selected in either the active or memory locations of the radio. The radio is equipped with a keyed entry pad for frequency selection, as well as two SCAN buttons which are used to scan either up or down the available frequency spectrum. These buttons protrude from the face of the radio and are activated by pressure contact. Safe VFR flight is predicated on the see and avoid principle. The effectiveness of this procedure in collision avoidance is dependent on flight crew detecting other aircraft on collision courses and on the pilots' abilities to take evasive action in time to avoid an in-flight collision. A pilot's ability to visually detect another aircraft is affected by many factors, including, the pilot's awareness of the presence of another aircraft, the pilot's available field of view, obstructions to that field of view, aircraft conspicuousness, pilot scanning techniques, and normal physiological limitations of the human visual and motor-response systems. In general terms, assuming that a pilot is looking in the correct direction, general aviation aircraft similar to the ones involved in this occurrence should, under good conditions, be detectable at an approximate range of 1 to 1.5 nautical miles. Contrast with the background, aircraft attitude, and the relative flight path of an aircraft can affect this detection range, often reducing it significantly. The human visual system has physical limitations that can reduce its performance. For example, the human eye is particularly attuned to detect movement but is less effective at detecting stationary objects. However, because of the geometry of collision flight paths, an aircraft on a collision course will appear to be a stationary object in the pilot's field of view. The use of high intensity strobe lights, anticollision lights, landing lights, and navigation lights, as well as high contrast paint schemes all help in making an aircraft more visible to others. Aircraft and cockpit designs can affect a pilot's ability to see effectively. Airframe structures such as wings, window posts, and engine cowls, as well as crew or passenger seating locations may mask certain areas around the aircraft from the pilot's view. It is generally recognized that traffic advisories will improve a pilot's ability to visually acquire another aircraft. First, the advisory provides advance warning of a potential conflict and will tend to increase the time that the crew will devote to the visual search for the traffic. Second, the advisory will aid the pilot in concentrating the visual search in the proper direction. Research indicates that, if alerted to the presence of another aircraft, a pilot is eight times more likely to acquire the target.(2)